1. Field of the Invention
This invention relates to a mechanism for lowering a casing slip into a bushing bowl and for subsequently lifting the casing slip out of the bushing bowl, and in particular to a mechanism that uses hydraulic cylinders to lower and raise the casing slip.
2. Description of Related Art
Casing slips have conventionally been lowered into and lifted out of a drilling hole manually. Since casing slip insertion and removal must be repeatedly carried out in order to lock and release successive casing sections during deep well drilling operations, such as oil well drilling, difficulties in removing the casing slips can add significantly to drilling costs.
Devices for automatically lifting and lowering casing slips have previously been proposed, but all require integral or modified bushing bowls and/or casings. Examples of such powered slip assemblies, which integrate the bushing bowl and casing slip, and which lift the casing slip so as to enable removal of at least elements of the casing slip from the integrated bushing bowl, are disclosed in U.S. Pat. No. 4,253,219 (Krasnov); U.S. Pat. No. 3,760,469 (Brown); U.S. Pat No. 2,641,816 (Liljestrand); and U.S. Pat. No. 2,030,087 (Young). While such mechanisms lift the casing slip sufficiently to enable disengagement, they are not capable of lifting the casing slip completely out of the bushing bowl, are relatively complex and/or difficult to implement, and furthermore the mechanisms themselves must be lowered and lifted, resulting in an increase rather than a decrease in the effort required to manipulate the casing slip.
In contrast, the present invention provides a hydraulically actuated lift mechanism that is intended to lift a casing and allow the casing slip to completely clear the bushing bowl, without modifying or integrating the bushing bowl that cams the casing slips into gripping engagement with the casing section. None of the above-cited patents, or any of background U.S. Pat. No. 6,227,587 (Terral); U.S. Pat. No. 4,511,168 (Haynes); and U.S. Pat. No. 4,275,488 (Gray), while U.S. Pat. No. 6,224,112 (Eriksen); U.S. Pat. No. 5,669,653 (Penisson); U.S. Pat. No. 5,301,750 (Watkins); and U.S. Pat. No. 4,340,116 (Weise), discloses such a mechanism.